The aspects of the present disclosure relate generally to wireless communication systems, and in particular to optimizing parameter setting for handover of mobile terminals on a transportation platform.
A cellular or wireless communication network generally includes a large number of cells. A cell, also may be referred to as a base transceiver station or a base station, may be generally defined as a fixed-location transceiver. When a user is communicating via a mobile terminal or device such as a cellular telephone, a communication link is established between the user's device and a cell. However, a cell has a limited area of communication or network coverage (also referred to range). Thus, a network is typically made up of a number of cells. As the user device moves from one cell (a source cell) to another cell (a target cell), a procedure referred to as “handover” or “handoff” is used to establish a new communication link between the user and the target cell and drop the communication link between the mobile device equipment and the source cell. A handover is generally triggered when the current connections of the user's device do not meet the radio connection's requirements in terms of signal strength. The changing of the connections during the handover operation can be affected by configuration of the handover procedures and the setting or parameters corresponding to the user's communication device and the cells.
In a Long Term Evolution (LTE) network, a handover is typically initially triggered by a measurement report sent from a user equipment to a serving eNB (evolved nodeB) or a serving cell. The serving eNB determines how the user equipment shall take measurements and under what conditions a measurement report shall be triggered and sent to the eNB. Different networks and network deployments can have different detailed behavior, but in most cellular networks it is natural to trigger handover when the signal reception from the target cell is stronger than the signal reception of the source cell. In the measurement report, the user equipment includes the reason for the handover trigger (e.g. target cell signal stronger than source cell) and measurements of the reference signal strength (RSRP) or quality (RSRQ) of the serving cell and several neighboring cells (including the target cell). To reduce ping-pong effects where the user equipment hands over repeatedly between two cells, a handover offset is added to the trigger condition. The signal from the target cell should be stronger than the signal from the source cell by a predetermined offset, such as greater than 0 dB, for example. Additionally, a timer can be used.
When a group of mobile terminals travel on a common transportation platform (CTP), such as a bus, light rail vehicle, or train, the mobile terminals share similar mobility characteristics. Normally, the handover of such mobile terminals have a significant impact on the total handover performance and perceived quality of experience and service, due to the relatively large proportion of mobile service usage by such mobile terminals.
For mobile terminals on a common transportation platform, the handover procedure can be designed so that optimal handover performance is achieved through utilization of the handover performance knowledge of the mobile terminals. Handover of mobile terminals on a CTP should be executed at optimal time for each mobile terminal to avoid signaling congestion. The preparation of the target cell (such as data forwarding in a 3GPP Long Term Evolution (LTE) handover procedure) can be done in advance, for each of the mobile terminals on the CTP. Information as about e.g. the route and velocity of the mobile terminals on the CTP and information about neighboring cell relations can also be utilized in the handover procedure.
Generally, when a number of handover failures occur, this can be typically caused by non-optimal handover parameter configuration and settings. The parameters can include for example, but are not limited to, received power offset between neighboring cells for handover purposes, often referred to as the signal strength hysteresis, and the time to trigger which represents a delay in sending a handover measurement report once the signal strength hysteresis has been met.
Generally, one way of optimizing handover parameters is to run an off-line optimization algorithm within an Operation and Administration Maintenance (OAM) system, and obtain optimal parameters solution for that handover failure problem. The new parameters can be set to the network, including network entities and terminals. Field engineers may run tests before the new parameters are formally committed. However, this process is slow and handover failures will continue to occur during this optimization process. Furthermore, the proposed parameters may be non-optimal by the time of implementation due to the time required to develop the new parameters and commit them to the system, and the need for continuous fine tuning.
Generally, conventional handover processes do not consider the characteristics for a group of mobile terminals with similar mobility behavior. It would be advantageous to be able to utilize the mobile terminals on a CTP for statistics collection in handover performance monitoring as well as an optimization process of setting and testing of handover parameters.
Accordingly, it would be desirable to provide an access and handover process within a communication network that solves at least some of the problems identified above and gain the advantages identified above.